In the past most hoisting devices used for lowering lifeboats and the like relied on a winch operator to lower a boat so that the boat reached the surface when the water level is rising rather than falling away. Otherwise the wave falls away under the boat so it is suspended by the cable again. It is also necessary to prevent slack occurring in the hoisting cable. If slack does occur, then when the wave falls away, the slack is taken up and a violent jerk occurs as the weight of the lifeboat is taken by the cable. This jerk action may cause undue stresses in the hoisting cable or in the hoisting connections to the lifeboat. Furthermore, such an action causes discomfort to passengers in a lifeboat.
Various types of winches have been devised to prevent the occurrence of slack in a cable and to prevent the jerk that occurs when the slack is taken up. One such hoisting device is disclosed in U.S. Pat. No. 4,928,925 which discloses a constant tension hoisting member with a separate cable tension sensing system. The hoisting device provides an automatic launching operation but not an automatic recovery arrangement. The winch disclosed in this patent utilizes a main motor and an auxiliary motor.
An aim of the present invention is to provide a winch for launching and recovering an object such as a boat from an active wave environment generally moving relative to a stationary or moving platform where the winch has a number of operational modes which operate separately from a manual operational mode. The operational modes include a launch mode, a motion compensation mode, a free wheel mode and a recovery mode.
It is a further aim of the present invention to provide a motion compensation winch which has a single hydraulic motor and utilizes primary and secondary gear reductions with primary and secondary clutches and incorporates a rotational sensor to sense when the load on the cable is either being raised or lowered by the wave and a load sensor to determine when the load on the cable is above or below a predetermined value. Both the load sensor and the rotational sensor are built into the winch, thus the winch is a completely independent unit suitable for retrofitting to any lifeboat davit or crane. There is no external cable tensioning device needed.
A still further aim of the present invention is to provide a motion compensation mode for a winch so that when a load has been launched and is supported by the water, the winch control lever may be placed in the hoisting position and the cable drum will take up the cable when the load rises and release the cable when the load lowers, always maintaining a tension on the cable. This motion compensation mode is used when a lifeboat or a buoy has been launched and prevents the object from drifting away from the launch platform.
There is also a recovery mode to recover a lifeboat or a buoy from an active wave environment, the load is recovered from the crest of a wave automatically without the operator having to pick the right moment. The recovery mode is selected when the winch is in the compensation mode, regardless of whether the load is rising or falling. The load is automatically recovered from the crest of a wave after rising up on the wave, once recovered, the winch is controlled in manual mode by operating the winch control lever.